The mixture of two racemates of the formula I', below, is commercially available. ##STR5## see S. Arctander, Perfume and Flavor Chemicals I, Montclair, N.J. 1969, item 1581. As is apparent from the structure of I', there are asymmetric carbon atoms at positions 4 and 7. Since the structure can be either in the R- or S- configuration at each of the asymmetric carbon atoms, there are four diastereoisomers corresponding to formula I' in the known commercially available mixture.